1. Field of the Invention
This invention pertains to devices for attracting fish and more particularly to such devices which emit acoustical signals to attract game fish.
2. Prior Art
It has long been known that acoustical signals are both generated and detected by fish and are important communications media for fish. A wide range of species of fish emit sounds and several species are known to be acutely sensitive to underwater sounds. Vibratory disturbances or underwater sound are detected through a specialized sense organ known as the acoustic-lateral line. Certain species appear to transmit an acoustical signal unique to the species and equivalent to a "signature." In addition, it has long been known that game fish behavior is modified during periods of weather disturbances which create sounds transmitted from the surface (e.g., wind, surf, rain, etc.) which may be referred to as "weather signatures." Sound production occurs in fish as part of their normal social behavior or when disturbed by a predator or subjected to other stimuli. Many fish produce calls as part of a particular behavior and the sounds are believed to elicit a change in the behavior of other fish of the same or different species. Calls may be made by stridulatory sounds produced by fish rubbing hard parts of the body together and resulting in a series of very rapidly produced and irregular transient pulses, containing a wide range of frequencies. Certain species of fish produce grating sounds, others produce squeaking or clapping or thumping sounds. A particular sound is produced by fish swimming or rapidly turning. Injured or distressed prey may produce sound signatures recognizable by predator fish. In certain species, different calls may be produced in different contexts and variations in calls may be in the form of pulse modulation or changes in the frequency structure. Studies have shown that certain fish species emit specific vibratory disturbances in the context of social behavior, such as social aggregation, and different vibratory disturbances in association with reproductive behavior. Certain predatory fish appear to be adept at detecting sounds, and particularly adept at homing in on the signature of a particular species of prey. There are studies which suggest that fish are able to discriminate among calls by distinguishing between signals on the basis of differences in frequencies as well as pulse rates, and even able to distinguish between signals that differ only in amplitude. Experiments have shown fish generally are sensitive to sounds only in the low-frequency range, below 10 kHz, and many species are sensitive only to sounds below 500 Hz.
For many years, the fishermen have attempted to produce underwater sounds in order to attract fish, and hopefully fish of a particular type, by means of lures that produce a vibration underwater. A number of vibrating lures have been proposed in the prior art which purport to attract fish by electrically or mechanically generating and transmitting signals of different pulse rates or different frequencies. However the prior art devices generate basically repetitive signals with no particular relationship to the comparatively complex signal structure emitted by fish. Particularly, the prior art devices do not provide a means for accurately generating signals which correspond to sound produced by a selected species of bait, such as is desirable in attracting certain species of game fish. The following are examples of prior patents directed to underwater signal-producing devices.
The prior patent, U.S. Pat. No. 2,784,399 to T. P. Smith (dated Mar. 5, 1957) discloses a sound producing fishing lure for transmitting sounds through the water. The lure includes an electromagnet and a vibrating armature contacting a metallic diaphragm to produce a buzzing sound. An inertia-responsive mercury switch causes the electromagnet to be operated intermittently, on a random basis, as the orientation of the lure changes due to wave motion or the like.
The U.S. Pat. No. 2,920,318 to H. A. Balcken et al. (dated Jan. 5, 1960) discloses a fish caller in the form of a cylindrical device adapted to be suspended from a fish line or the like. The unit includes a buzzer provided with a screw adjustment to regulate the pitch of the resulting sound produced by the buzzer.
The U.S. Pat. No. 4,583,313 to C. J. Duggan, Jr. (dated Apr. 22, 1986) discloses a fishing lure intended to emit signals of different frequencies in order to attract the fish of a particular species. The lure is described as employing a piezoelectric transducer driven by an integrated circuit oscillator adjustable to produce various frequencies in a range from 1 Hz to 100 kHz by the changing of circuit components.
The U.S. Pat. No. 4,805,339 to Fuentes et al. (dated Feb. 21, 1989) discloses a sonic fishing lure employing a pair of astable multivibrators to produce underwater sound. A 1 Hz and a 100 Hz multivibrator are used together to provide intermittently pulsed outputs at approximately 100 Hz for a duration of approximately 700 milliseconds separated by non-sound producing time periods of approximately 200 milliseconds.
A limitation of the these and other prior art devices is that while they produce underwater sounds purported to attract fish, it is not known whether the sounds produced by the prior art lures correspond to sounds of bait to which game fish respond. Furthermore, fish appear to produce acoustical signals which vary in signal frequency, periodicity and amplitude. Such complex signals are not readily reproduced by buzzers or other devices which generate signals of fixed frequency, duration and amplitude or which are varied in an arbitrary manner. Prior art lures generally have lacked an effectiveness in attracting fish. An apparent reason is that the appropriate complex acoustical signal patterns to which fish react have not been generated by the prior art devices. Studies have shown that certain game fish have a preference for and seem to be able to select certain bait fish, presumably on the basis of acoustical signals transmitted by the bait fish which allow the predator to discriminate among the bait. Acoustical patterns which allow such discrimination do not appear to be generated by prior art lures.